Application of Light Stabilizers in Plastic Products

Light stabilizers are key additives used in outdoor and light environments for plastic products. By absorbing, shielding, or quenching ultraviolet energy, they inhibit the oxidative degradation, molecular chain breakage, and cross-linking reactions of plastics caused by ultraviolet radiation, avoiding problems such as discoloration, brittleness, cracking, and mechanical performance degradation of products. The C-C bonds and C-H bonds in plastic molecular chains are easily damaged by ultraviolet light (especially near ultraviolet light at 290-400nm). For example, PE films without added light stabilizers can become brittle after 6 months of outdoor use, while the service life can be extended to 3-5 years after adding light stabilizers. It is compatible with almost all plastic categories such as PE, PP, PVC, PET, PC, etc. According to its mechanism of action, it can be divided into four categories: UV absorbers, quenchers, shielding agents, and free radical scavengers. Currently, it is developing towards high efficiency, low migration, and multifunctionality, becoming the core guarantee for plastic products to achieve long-term outdoor use.

1、 The core mechanism of action of light stabilizers: precise blocking of the UV aging chain

Plastic UV aging is a synergistic process of "photo oxidative degradation". UV radiation first triggers molecular chain breakage to produce free radicals, which react with oxygen to accelerate degradation. Light stabilizers intervene in different stages to construct a full chain protection system:

1. UV absorbers: absorb energy and convert it

Ultraviolet absorbers (UVA) can selectively absorb ultraviolet light at 290-400nm, converting light energy into harmless heat energy for release, avoiding UV excitation of plastic molecular chains

Representative products: Benzotriazole (UV-327, UV-326), Benzophenone (UV-531);

Action pathway: Chromogenic groups in the molecular structure (such as triazole rings and carbonyls) capture ultraviolet energy and convert it into thermal energy through intramolecular vibration, maintaining their stable structure and allowing them to function cyclically;

Adaptation scenario: Transparent plastic products (such as PET beverage bottles, PC lampshades) that do not affect the transparency of the product.

2. Quenching agent: Transfer of excited state energy

Quenching agents (such as nickel complexes) mainly act on plastic molecules (excited state molecules) that have been excited by ultraviolet light, restoring them to their ground state through energy transfer and avoiding molecular chain breakage:

Representative products: Nickel dibutyldithiocarbamate, nickel complex UV-1084;

Action pathway: Collide with plastic excited state molecules, capture their excited state energy and release it in the form of vibrational energy, forming a stable complex structure on its own;

Adaptation scenario: Dark colored plastic products (such as black PP car bumpers) have strong weather resistance but poor transparency, and are not suitable for transparent products.

3. Shielding agent: physically blocks ultraviolet rays

Shielding agents prevent ultraviolet rays from penetrating the interior of plastics by reflecting or scattering them, forming a physical protective barrier:

Representative products: Carbon black, titanium dioxide, zinc oxide nanoparticles;

Action pathway: Carbon black achieves shielding by absorbing ultraviolet light, while titanium dioxide and zinc oxide exert their effects by scattering ultraviolet light. Nanoscale particles can reduce the impact on the mechanical properties of the product;

Adaptation scenario: Opaque plastic products (such as PE water supply pipes, PVC pipes), low cost but may change the color of the product.

4. Free radical scavenger: terminates the degradation chain reaction

Free radical scavengers (such as hindered amine light stabilizers HALS) target the chain reaction of free radicals induced by ultraviolet radiation, capturing and terminating free radicals, and blocking the degradation cycle:

Representative products: HALS 770, HALS 944;

Action pathway: It combines with the free radicals generated by plastic degradation to form stable nitrogen oxygen free radicals, while regenerating itself to continuously capture and have antioxidant function;

Adaptation scenarios: Various plastic products, especially those suitable for long-term outdoor use (such as agricultural films, outdoor building materials), with high protection efficiency.

2、 Mainstream light stabilizer types and compatible plastics: precise matching of characteristics and scenarios

Different light stabilizers have significant differences in transparency, heat resistance, compatibility, and toxicity. The selection should be based on the type of plastic and application scenario (such as transparency requirements, food contact, outdoor life). The following are the four core categories:

1. UV absorbers (UVA): preferred for transparent products, low toxicity and universal use

UV absorbers are the most widely used type of light stabilizer, with low toxicity (mostly meeting food contact standards), good compatibility, and no impact on product transparency. The addition amount is usually 0.1% -0.5%:

Benzotriazole class: excellent heat resistance (processing temperature ≤ 280 ℃), high UV absorption efficiency, suitable for PE, PP, PET, PC;

Typical applications: PET beverage bottles, PC laptop shells, transparent PP meal boxes, can prevent products from yellowing and discoloration.

Benzophenones: Low cost, moderate weather resistance, suitable for PVC, PE, ABS;

Typical applications: PVC film, ABS household appliance shell, the disadvantage is that it is prone to volatilization at high temperatures, and the processing temperature needs to be controlled.

2. Hindered amine light stabilizer (HALS): long-lasting protection, multifunctional integration

HALS is currently the most efficient light stabilizer for protection, with both light stability and antioxidant functions. It has strong long-term performance (outdoor protection period can reach 5-10 years), and the addition amount is usually 0.2% -1.0%:

Low molecular weight HALS (such as 770): good compatibility, fast onset, suitable for PE and PP;

Typical applications: PE agricultural film, PP woven bags, the disadvantage is that the migration rate is high, and the protective effect deteriorates after long-term use.

High molecular weight HALS (such as 944): low mobility, outstanding long-term performance, suitable for PET, PC, PA;

Typical applications: PET pipes, PC outdoor lampshades, PA automotive parts, can meet the long-term protection needs of high-end products.

3. Quenching agent: specialized for dark colored products, with strong weather resistance

Quenching agents are mainly used for dark plastic products, with high protection efficiency but poor transparency. The addition amount is usually 0.1% -0.3%:

Representative products: Nickel complexes, suitable for PP, PE, PVC;

Typical applications: Black PP car bumper, dark PE water supply pipe. The disadvantage is that some nickel complexes are toxic and limited for use in the food contact field.

4. Shielding agent: low-cost protection, suitable for opaque products

Shielding agents have low cost and direct protective effect, with a typical addition amount of 1% -5%. However, they can change the color of the product and may affect its mechanical properties

Carbon black: has strong UV absorption ability and also has antioxidant function, suitable for PE and PP;

Typical applications: Black PE agricultural drip irrigation pipe, PP outdoor garbage bin, with no obvious aging after more than 3 years of outdoor use.

Nano oxides (TiO ₂, ZnO): scatter ultraviolet light, can be used for light colored products, suitable for PVC and ABS;

Typical applications: Light colored PVC door and window profiles, ABS outdoor fitness equipment, need to control particle dispersion to avoid affecting product strength.

3、 Application Practice of Light Stabilizers in Key Plastic Products: Scenario based Formula Design

The usage environment and performance requirements of different plastic products vary greatly. The formulation of light stabilizers needs to be customized based on "plastic type - light intensity - service life - appearance requirements". The following are typical cases:

1. Polyolefin products (PE, PP): Core protection for outdoor products

PE and PP are the mainstream materials for outdoor plastic products, which are susceptible to UV aging. The commonly used "UVA+HALS" compound system enhances the protective effect

PE agricultural film:

Formula: UV-327 (0.2%)+HALS 770 (0.3%)+antioxidant 1010 (0.15%);

Effect: After 12 months of outdoor use, the light transmittance retention rate is greater than 85%, and the tensile strength retention rate is greater than 70%, avoiding premature cracking and ensuring the growth needs of crops.

PP car bumper:

Formula: HALS 944 (0.5%)+UV-531 (0.2%)+antioxidant 168 (0.2%);

Effect: Outdoor use for 3 years without discoloration or cracking, with a retention rate of impact strength greater than 80%, meeting the weather resistance requirements of automotive components.

2. Engineering plastic products (PET, PC): Balancing transparency and long-term effectiveness

Engineering plastics such as PET and PC are commonly used in transparent products, which require high transparency and heat resistance of light stabilizers

PET beverage bottle:

Formula: UV-326 (0.15%)+antioxidant 1010 (0.2%);

Effect: It prevents the beverage from spoiling due to ultraviolet rays, while avoiding yellowing of the bottle body. After 6 months of storage, the light transmittance should be greater than 90%.

PC outdoor lampshade:

Formula: UV-327 (0.3%)+HALS 944 (0.4%);

Effect: Resistant to outdoor ultraviolet radiation for 5 years, with a transmittance retention rate of over 80%, no cracking or discoloration, ensuring lighting effectiveness.

3. Food contact plastics: low migration and low toxicity as the core

Food contact plastics (such as PP lunch boxes and PE cling film) have strict requirements for the toxicity and migration of light stabilizers, and products that comply with GB 4806.6 and EU No. 10/2011 standards should be selected

PP Microwave Meal Box:

Formula: UV-327 (0.1%)+antioxidant 1010 (0.1%);

Effect: Resistant to ultraviolet radiation with a migration rate of less than 0.01mg/kg, meeting food safety standards, and no harmful substances released during microwave heating.

PE food preservation film:

Formula: UV-531 (0.08%)+antioxidant 1076 (0.08%);

Effect: Store at room temperature for 3 months without aging or brittleness, with no risk of migration when in contact with food, ensuring food freshness.

4. Building materials and plastic products: Long lasting and durable, suitable for extreme environments

Building materials plastics (such as PVC doors and windows, PE water supply pipes) need to withstand extreme outdoor temperatures, humidity, and ultraviolet radiation for a long time. The formula of light stabilizers focuses on long-term durability and weather resistance:

PVC door and window profiles:

Formula: Carbon black (2%)+UV-531 (0.3%)+Calcium zinc composite heat stabilizer (2%);

Effect: There is no significant aging after 10 years of outdoor use, and the retention rate of tensile strength is greater than 65%, meeting some requirements for a 50 year service life of building materials.

PE water supply pipe (buried+outdoor section):

Formula: HALS 944 (0.6%)+carbon black (3%)+antioxidant 1010 (0.2%);

Effect: The outdoor section is resistant to ultraviolet radiation, the buried section is resistant to microbial corrosion, and the overall service life is up to 50 years.

4、 The development trend of light stabilizers: high efficiency, environmental protection, and multifunctionality

With the development of plastic applications towards high-end (such as new energy vehicles, high-end building materials) and environmental protection (biodegradable plastics), light stabilizers need to break through traditional limitations and present three core trends in the future:

1. Efficient and low migration type: suitable for high-end scenarios

Traditional light stabilizers are prone to migration during high temperatures or long-term use, leading to a decrease in protective effectiveness. In the future, we will focus on developing high molecular weight and reactive light stabilizers:

High molecular weight HALS (molecular weight>2000) reduces migration through molecular chain entanglement, and the migration amount in PP automotive parts is 80% lower than that of ordinary HALS;

Reactive light stabilizers (such as UVA containing acrylate groups) can undergo chemical reactions with plastic molecular chains, fundamentally solving migration problems and adapting to food and pharmaceutical packaging scenarios.

2. Biobased light stabilizers: in line with green policies

A bio based light stabilizer made from plant extracts such as rosemary extract and tea polyphenol derivatives, with extremely low toxicity and biodegradability, in line with the "dual carbon" policy:

Rosemary extract light stabilizer is used for PE agricultural film, with a protective effect equivalent to UV-327, and can be biodegraded after disposal without environmental residue;

Tea polyphenol derivative light stabilizers are suitable for PP food packaging, while also possessing antibacterial functions, expanding their application value.

3. Multi functional integration: simplifying formulas and reducing costs

The traditional protective system requires a combination of "light stabilizer+antioxidant+heat stabilizer", and in the future, multifunctional integrated additives will be developed:

HALS containing antioxidant groups can achieve both photostability and antioxidant functions simultaneously. In PE outdoor products, the total amount of additives added is reduced from 1.0% to 0.6%;

Light stabilized antibacterial composite additive is used for ABS outdoor fitness equipment, which not only resists UV aging but also inhibits bacterial growth, enhancing product added value.

5、 Summary: Light stabilizers - the "longevity code" for plastic outdoor applications

From daily PE cling film and PP meal boxes, to industrial PET pipes and PC electronic components, to outdoor PVC doors and windows, PE agricultural films, light stabilizers precisely block the UV aging chain, ensuring the stable performance and service life of plastic products in light environments. It is not only an "anti-aging additive", but also has a direct impact on the economy (extending the service life to reduce replacement costs), environmental protection (reducing plastic waste) and safety (avoiding harmful substances from aging degradation) of plastic products. In the future, with breakthroughs in the research and development of high-efficiency, low migration, bio based, and multifunctional light stabilizers, it will further promote the development of the plastic industry towards "long-term and green", adapt to more high-end application scenarios, and provide solid support for the outdoor expansion of plastic products.